The present invention is described by its use with a video display device but it should be understood that other output devices, such as a printer which handles serial information can employ the present invention.
It is generally the practice in the video display art (in order to display information on a video screen), to store information in a memory device and read said information therefrom into a shift register. The shift register is stepped in synchronism with the scan rate of an electron beam in the CRT. If the pixel information indicates that a dot should be present on the CRT, the beam will be turned on and if the pixel information indicates that a dot should not be present then the beam will be turned off. In the prior art, video display manufacturers have commenced employing bit map memory devices and in particular bit map memory units formed on integrated circuit chips. The bit map memories have the advantage that for each pixel location on the face of the display means, there is a pixel location in memory. Hence, the pixel information in the bit map memory can be read out to paint the picture, or to paint an alpha-numeric display, on the screen, without necessitating a great number of manipulations of information and accordingly very rapidly. However the state of the art has advanced such that pixel information is available (and desirable) from a number of pixel information input means. A major problem is that the pixel information sources operate at different speeds and very often the information signals are burdened with phase distortion, jitter, timing irregularities and the like. If such information is used directly from the source to the video display, the picture provided to the viewer is often unsatisfactory. In addition, with the introduction of high resolution display devices, (including means that provide varying character intensities and color presentations), the operational speeds of the shift registers and memories have represented limitations. Further as the video display systems have become more sophisticated, the demand has increased for: high resolution devices; full screen scrolling operations; window scrolling operations; the use of multiple video information sources, and the like. Heretofore there has not been a compact, flexible arrangement to accomodate the foregoing demands, particularly with the capability of being disposed on an integrated circuit chip. The present system provides a multiport memory means as well as a flexible signal routing means which enables the operations, enumerated above, to be effected as well as other operations and is compact enough to be disposed on an integrated circuit chip.